The present invention relates to a heat exchanger which is used for air conditioning, refrigeration and the like and which is adapted to perform transmission and reception of heat between fluids.
Conventionally, the heat exchanger of this type has comprised copper tubes connected to each other with U-bent pipes, and aluminum fins so that a heat exchange operation is performed between a cooling medium flowing through the copper tubes and air flowing among the fins.
Recently, this type of heat exchanger has been required to be miniaturized and to have a more improved efficiency, but at present the velocity of air flowing among the fins is forced to be kept at a low speed due to problems such as noise and the like. The thermal resistance of the air around the heat exchanger is extremely high as compared to that of the fluid in the copper tube. Accordingly, to reduce the difference in the thermal resistance between inside and outside the copper tubes, the heat transfer area of the heat exchanger on the outside of the copper tubes, i.e., on the side of the air is made comparatively large when compared to the transfer area inside the tubes. However, the enlargement of the heat transfer surface of the heat exchanger is limited to a certain degree, and therefore, even when the transfer area on the outside of the tubes is made large, the thermal resistance on the inside of the tubes is far higher than that on the outside of the tubes.
Accordingly, attempts have been made to apply suitable processes on the surface of each fin for the reduction of the thermal resistance between the air and the fin.
An example of a prior art heat exchanger is shown in FIGS. 2(a) and 2(b). The surface of the fin is processed to have air vents, i.e., the fin has interrupted plate passages, so that the thermal resistance of the surface of the fin is lower by 40-50% than that of the ordinary flat plate fin. In FIG. 2(a), a numeral 5 designates fin collars, a numeral 6 designates a fin, numerals 7a and 7b designate bridgelike air vents and a numeral 8 designates the flow direction of air. A cooling medium flows through the copper tubes 4 and the heat of the cooling medium is transmitted from the fin collars 5 fitted about the copper tubes 4a and 4b to the fin 6 and the bridgelike air vents 7a and 7b.
At the same time, the air supplied from the direction of the arrow 8 by means of a fan or the like passes among the fins 6 and exchanges heat with the surfaces of the fins of a temperature different from that of the air thereby allowing a heat exchange operation to be performed continuously between the cooling medium and the air. The fin 6 having the louverlike air vents 7a and 7b can have a surface thermal resistance lower than that of a fin having no such air vents because of the leading edge effect but the following problems have not yet been solved satisfactorily.